I got a D500 from Nikon USA refurbished site less than two weeks ago. Two days ago it started acting up. (Unfortunately NR does not allow direct uploads so I can show the photos). On one evening's shoot about a dozen photos in the middle of the sequence had a black bar intruding into the photo. It was the shape of a wide blade of grass, with the end slighly wider than the base (the end stopped just past middle of frame but the base extended beyond the edge of the frame). In some cases it was tack sharp and in some a bit blurry. When I saw this after uploading the photos on my computer I turned on the camera to do test shots. First one had the bottom third of the photo black and rest normal (like when you use too fast of a shutter speed with a flash, except of course I was not using a flash on this or any previous photo). Second shot the black covered just over half the bottom. Third photo the black covered almost the entire frame, with just a sliver (maybe 1/16th) of the photo showing on the top. I turned off the camera and reattached lens and it seemed to work fine. So I went back out next night and did some test shots in the field and at first fine but after a while the same thing where most of image was black and only a sliver at top showed.
I came home, turned camera on again, and have taken several shots inside and so far not been able to replicate the problem. I am just curious if anyone has had similar issues with D500 and if you know if this is a shutter malfunction (which I assume) or a lens malfunction. I have been using the same lens for months on my D850 with no issue.